The present invention relates to a heat insulator for a carburetor, and more particularly to a heat insulator adapted to be mounted between a downflow type carburetor and an intake manifold.
In operation of a carburetor, the wall of a throttle bore of the carburetor is generally covered with a film of liquid fuel formed by the attachment of fuel droplets and the fuel film gradually flows along the wall surface of the throttle bore toward an intake manifold connected with the carburetor. However, the fuel film is generally not uniformly distributed around the periphery of the wall of the throttle bore, due to the effect of the direction of fuel ejection from the main and auxiliary fuel nozzles in the carburetor, the asymmetrical arrangement of the throttle valve, etc., whereby there occurs an unbalance in the fuel supply to individual cylinders caused by the fuel film flow which is conducted along the inner wall surface of the throttle bore and the intake manifold thereby causing an irregularity of air/fuel ratio between the various cylinders. In current engines the variation of air/fuel ratio between individual cylinders is relatively high, amounting, in some instances, to .+-.20% deviation from the mean value. Such an irregularity in the supply of fuel to individual cylinders causes various drawbacks such as poor engine efficiency, poor fuel consumption, increase of octane requirement and unstable operation in idling and low load conditions.